This invention relates generally to rotary devices. More specifically, this invention relates to outer envelope trochoidal rotary devices.
Trochoidal rotary devices are constructed so that a rotor assembly planetarily rotates in a housing defining a cavity. Trochoidal rotary devices can be divided into two groups: inner envelope trochoidal devices; and outer envelope trochoidal devices. In an inner envelope trochoidal device, the rotor assembly includes apex seals, side seals, and button seals that cooperate with the inner walls of the housing that define the cavity to define a plurality of discrete chambers. In an outer envelope trochoidal device, the apex seals, side seals, and button seals are mounted in the inner wall of the housing, the apex seal being mounted between the individual working chambers. Accordingly, the peripheral surface of the rotor assembly cooperates with the apex seal to define a plurality of discrete chambers. The peripheral surface of the rotor assembly and inner wall of the housing function as working chambers for expansion engines, compressors, expanders, meters, etc.
The side seals cooperate with the button seals to seal the rotor and the housing between the sides thereof. In an internal combustion engine this is important to prevent gas leakage from the working chambers. The side seals also cooperate to prevent oil leakage from the rotor shaft into the working chambers. The button seals function to complete the seal grid on the housing between the rotor and side wall of the housing; to this end, the button seals cooperate with the apex seals to provide a seal for the working chambers.
In order to afford a tight seal, the button seals are biased against the rotor. To create a sufficiently strong seal grid, a given pressure (i.e., pounds per square inch) must be exerted by the button seal against the apex seal and rotor. A certain force is required to counteract any lifting which could occur if gas pressure gets under the seal. The spring force exerted by the button seals must equal or exceed the potential gas force in case the seal lifts off the contact surface of the rotor. Accordingly, the larger the surface area of the button seal that abuts the rotor, the larger the force exerted by the button seal against the rotor. This results in a corresponding frictional drag against the rotor and therefore a corresponding loss in the efficiency of the trochoidal device.
For example, in an outer envelope trochoidal device having a trochoidal rotor having four lobes, the cavity of the housing defines the outer envelope of that trochoidal curve and accordingly has five concave portions. Therefore, five apex seals are disposed at the intersection of each of the concave portions. Because, a button seal must be located at each end of the apex seal, ten (10) button seals are located in such a trochoidal rotary device. As can be appreciated, because there are ten button seals, each incremental frictional drag force exerted by each button seal can result in a large frictional drag force on the rotor. Therefore, it is desireable to reduce the frictional drag of the button seals on the rotor assembly.
The side seals also provide a concern in some typical prior rotary devices. For example, some prior rotary devices have side seals that do not seal the side of the housing and rotor sufficiently tight and, accordingly, oil leaks into the working chambers. To counteract this problem, cut off a portion of the side seal and insert a filler piece in the gap. The filler piece extends from the remaining portions of the seal and contacts the rotor; the intent being that as the extended end is worn off a continuous seal along the length of the grid is effected. However, as the rotor heats up and cools, the filler piece slides up and down causing the filler piece to move within the gap and separate from the remaining portions of the seal. This results in a leak in the seal. Therefore, this side seal arrangement has not been entirely satisfactory.
Accordingly, there is a need for an improved seal arrangement for an outer envelope trochoidal device.